WASHINGTON — AARP‘s endorsement helped pass President Barack Obama’s health care overhaul. Now the powerful seniors’ lobby is telling employees their costs will go up as a result.

In an e-mail to employees obtained by the Associated Press, AARP says employees’ health care premiums will increase by 5 percent — from 8 percent to 13 percent — next year because of rapidly rising medical costs.

“Most plan co-pays and deductibles have been modified,” Jennifer Hodges, AARP’s director of compensation and benefits, wrote employees in the Oct. 25 e-mail. “Plan value changes were necessary not only from a cost management standpoint but also to ensure that AARP’s plans fall below the threshold for high-cost group plans under health care reform.”

AARP says it is also changing co-payments and deductibles to avoid a new goverment-mandated 40 percent tax on high cost “Cadillac” health plans that takes effect in 2018 under the law. Shifting costs to employees lowers the value of a health plan; it’s like an escape hatch from the tax.

Last year, the AARP reportedly lost 60,000 members who resigned membership in anger over the group’s support of the Democrats’ health care overhaul.